package risoe.syslab.fhnew.hw.enocean3;

/*
 * Copyright (c) 2012-2014, Technical University of Denmark (DTU)
 * All rights reserved.
 * 
 * The Flexhouse 2.0 platform ("this software") is licensed under the
 * BSD 3-clause license.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   - Neither the name of DTU nor the names of its contributors may be used to
 *     endorse or promote products derived from this software without specific
 *     prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE TECHNICAL UNIVERSITY OF DENMARK BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * Code courtesy of IoTSyS
 * https://code.google.com/p/iotsys/
 * @TODO put proper copyright header here
 */

public final class CRC8Hash
{
	private static final byte[] CRC8_TABLE = calculateCRC8Table();

	private CRC8Hash () {}

	private static byte[] calculateCRC8Table()
	{
		byte[] table = new byte[256];
		int generatorPoly = 0x07;
		int result;

		for (int i = 1; i < table.length; i++)
		{
			result = i;

			for (int j = 0; j < 8; j++)
			{
				if ((result & 0x80) != 0)
				{
					result = (result << 1) ^ generatorPoly;
				}
				else
				{
					result = result << 1;
				}
			}
			table[i] = (byte)result; 
		}
		return table;
	}

	public static byte calculate(byte[] data)
	{
		return calculate(data, 0, data.length);
	}

	public static byte calculate(byte[] data, int offset, int len)
	{
		byte crc = 0;

		for (int i = offset; i < (offset + len); i++)
		{
			crc = CRC8_TABLE[(crc ^ data[i]) & 0xFF];
		}
		return crc;
	}
}